Ophthalmic glass



Patented Sept. 26, 1950 OPHTHALMIC GLASS William H. Armistead, Corning, N. Y., assignor to Corning Glass Works, Corning,

poration of New York N. Y., a cor- No Drawing.- Application June 30, 1947,

' Serial No. 758,233

8 Claims.

1 This invention, which is a continuation in part of my pending application Serial Number 691,663

filed August .19 1946, now issued as-Patent 2,433,883, relates to transparent ophthalmic glasses, small buttons of which are to be sealed into lenses of crown glass for the production of multifocal spectacle lenses. lasses which are to be used for this purpose must meet certain requirements. Above all, they must seal properly with standard white optical crown glass which has a thermal expansion coefficient of 93 10 cm. per cm. per degree C. and a softening point of about 725 C. Softening point is that temperature at which a fibre of the glass of specified size will elongate under its own weight at a given rate when suspended through a small furnace of specified dimensions (Viscosity of Glass between the Strain Point and Melting Temperature, by H. R. Lillie, Jour. Am. Cer. Soc., Vol. 14, page 502, July 1931). They must have good devitrification resistance during sealing and adequate chemical durability or resistance to weathering. Their purpose requires an index of refraction for the D'line (1113) between 1.57 and 1.70 and it is desirable that they have a dispersive index (11) which is as high as possible. Prior ophthalmic glasses of high refractive index have a maximum dispersive index of about 32 which is less than desired. The prior glasses of lower refractive index have a maximum dispersive index of about 50 but have insufficient chemical durability.

The primary object of this invention is to provide ophthalmic glasses which have higher dispersive indices than have hitherto been obtainable in glasses of this type without sacrifice of other desirable properties.

Another object is to provide ophthalmic glasses having optical properties ranging from nD=1.70, preferably nD=1.65, 1 46, to nD=1.57, preferably nD=1.59, 11 53, but having at the same time good chemical durability, softening points below 700 C. and thermal expansion coeflicients between 83 and 95 10- cm. per cm. per degree C.

In general, I have found that the above objects may be attained withglasses comprising 33% to 60% SiOz, 1% to 70% B203, 2% to 15% ZIOz, to 25% BaO, .3% to 5% LizO, 1% to 15% NazO, 0% to PhD, and an oxide of at least one metal of the second periodic group whose atomic weight is between 40 and 113, namely, Ca, Zn, Sr or C'd, collectively amounting to from 3% to 30% but individually amounting to less than the glass containing at least two bivalent metal oxides and the total percentage of such bivalent metal oxidesbeing not less than 15% Y 2 and not over 50%. In lieu of NazO, K may be substituted Wholly or in part.

For the present pu'rpose'the outstanding fault of prior glasses is their high, dispersion for light of different wave lengths, that is, their low dispersive index, which causes excessive color aberration; Although it may be absent, the present glasses preferably should contain at least 5% BaO, because BaO raises the refractive index without unduly lowering the dispersive index.

More than 25% 32,0 may cause devitrification.

Since the use of BaO,,in. substantial amounts tends to raise the liquidus temperature of the glass objectionably, it is necessary to include one or more other bivalent oxides to prevent or counteract this. Other bivalent oxides which are useful for this purpose are PbO, Cao ZnO, SrO

and CdO.

CaO, ZnO, SrO and CdO also raise the refractive index They are particularly valuable for further increasing the refractive index without causing devitrification in glasses having large BaO contents, but may also be added to the glass irrespective of the presence or absence of BaO. Up to 15% of eachmay thus be employed, provided their total does not-exceed 30%. Other oxides, if desired, may be added with benefit as follows: r w 7 Up to'8% but preferably-not over 5% A1203 may be added, preferably butnot necessarily in lieu of S102. of the glass to devitrification.-

T102 may be incorporated in the glass with advantage to the optical properties and chemical durability. Both TiOz and ZI'OZ tendto raise the refractive index of the glass more than the other possible without unduly lowering thedispersiveindex. Upato 10% or, more 'TiO2 may thus be added a The expansion ,coeflicient for suitable sealing to the standard optical crown glass will vary somewhat with. softening point and with composition, and :thenew glasses willseal satisfactorily if theirexpansion coeflicients are be- Such addition increases the resistance tween -83 10- and 94 10-" cm. per cm. per degree C.

The following compositions in weight percentage as calculated from their batches are given by way of example but not as limitations of the invention:

12 12 6 10 Softening point, "C 690 670 691 699 Exp. Coefi. X 10 85 88 91" 92- 12B 1. 659 1. 660 1. 616 1. 680 v 45.3 45.5 49 4 43 2 It is characteristic .of the new glasses that they contain a substantial amount of ZrOz. Commercial Zr02 sometimes contains a small amount of uranium as an impurity which is sufficient to cause fluorescence in brightlight. This sometimes creates the appearance of an objectionable fog. or haziness before the eyes when spectacle; lenses composed of such; glasses are worn. in' strong light. I have found that;the"obiectionable 4 metal oxides being between 15% and 50%, the softening point of the glass being below 700 C., the refractive index (nD) being between 1.57 and 1.70 and the thermal expansion coefficient being between 83 and 95 10 cm. :per cm. per

C. between 0 and 300 C.

3. An ophthalmic glass. which comprises 33% to 60% .Si02, 1% to 7% B203, 2% to 15% Zr02, 0.3% to Li20, 1% to 15% of an alkali metal oxide selected from the group consisting of 112120,

K20,. and-mixtures of N220 and K20, and at least two bivalent metal oxides in the indicated proportions selected from the group consisting of 5% to'25%-Ba0, up to PbO, 3 to CaO, 3% to'15% ZnO, 3% to 15% SrO, and 3% to 15% 01:10, theselected bivalent metal oxides including BaO and CdO in the above-indicated proportions, the total of the bivalent metal oxides being between 15% and 50%, the softening point of the glass being below 700 C., the refractive index (nD) beingbetween 1.57 and 1.70 and the thermal expansion coefficient being between 83X 10" and 95 10' cm. per cm. :per 0. between 0 and 300 C.

4-. An ophthalmic glass which comprises 33% to-60% Si02, 1% to 7%13203, 2% to 15% ZrOz, 0.3% to-5% Li2O, 1% to 15%"of an alkali metal oxide iselected-from-the group consisting of Na20,

' K20, and mixtures of Na and K20; and at least fluorescence can be prevented? by melting the glass under reducing conditions or by the addition of a small amount of. SnOz; The latter decomposes sufficiently during, melting; to causereduction of the uraniumto a' lower valence which does not fiuoresce':

I claim:

1. An ophthalmic glass which, comprises33% t0 60% .5102, 1% to 7% B203; 2% to 15% ZIO2,

0.3% to 5% Li20, 1% to1'5'% of analkali' metal oxide selected from the group consisting of NazO, K20,'and mixtures'of Na2O'andK20, andat least two bivalent metal oxidesin the-indicated proportions selected from the group consisting of up to BaO, up to 10% PbO, 3% to 15% Geo, 3% to 15% ZnO, 3% to 15% S10; 3% t0-15% CdO, and 3% to ofa mixture of S10 and CdO, the maximum proportion ofeither'SrOor CdO in said mixture being 15%,the selected bi-. valent metal oxides including an oxide'selected from the group consistingoi SrO, CdO, and a mixture of SrO and CdO in the above-indicated proportion, the total of the-bivalent metal oxides being between 15% and 50%, the softeningpoint of the glass beingbelow'700 C., the refractive index 01D) being'bet'ween" 1.57 and" 1170arid-the thermal" expansion coefli'cient' being' between 83 10 and 95 10- cm; per cm. per C; between 0 C. and 300C.

2. An ophthalmic glass which comprises 33% to 60% S102; 1% t07 %"B203;'2% to 15% ZIO 2, 0.3%to 5% Li20, 1% to1'5%'0fan= alkali metal oxide selected from the group consisting'of' Na2O. K20, and mixtures of'Na2O" and K20, and at least two bivalent metaloxides in the indicated proportions selected from the group consisting ofup to 25% BaO, up to 10% P100; 3'%' to 15% CaO; 3% to 15% ZnO, 3% to 15% SrO, 3% to 15% 'CdO, and 3% to'-30% of a mixt'ure' of" SrQ-and H CdO, the maximum proportion of either SrO-or two bivalent metal oxides in the indicated pro portions selected from the group consisting of 5%-to 25% BaO, up to 10% PhD, 3% to 15% CaO, 3% to 15% ZnO, 3% to 15% SrO, and 3% to"15"%" CdO; theselected bivalent metal oxides including BaO and SrO in the above-indicated proportions, the totalof the bivalent metal oxides being between 15% and the softening point of the glass being below 700 C., the refractive index (nD) being between 1.57 and 1.70 and thethermal expansion coefficient being between 83 10' and- 95 10-- cmwper cm. per CLbetween 0 and 300 C.

5'. An ophthalmic glass which comprises 33% to Si02, 1% to 7% B203, 2% to 15% Zr02, 0.3% to 5% Li20, 1% to 15% of an alkali metal oxide selected from the group consisting of Na20, K20, and mixtures of Na2O' and K20, up to 8% A1203, and'at lease two bivalent metal ox=- ides in the indicated proportions selected from the' group consisting of up to 25% BaO, up to 10% PbO, 3% to 15% C20, 3% to 15% ZnO, 3% to 15% sro, 3%to 15% CdO, and 3% to 30% of a mixture of SrO and CdO, the maximum pro portion of either SrO or CdO in said mixture 7 being 15%, the selected bivalent metal oxides including BaO and an oxide selectedfrom the group consisting of Sr'O', CdO, and a mixture of SrO and CdO in the above-indicated proportions, thetotal of the bivalent metal oxides being between 15% and 50%, the softening point of the glass being below 700 0.. the refractive index ('nD)- being between 1.57 and 1.70 and the thermal expansion coeflic-ient being between 83X 10- and 10- cm. per cm. per C. between 0 and 6. An ophthalmic glass which comprises 33% to 60% Si02, 1% to 7% 13203, 2% to 15% 2102. 013% t'o'5% Li20, 1% to 15% of an alkali metal oxide selected from the group consisting of Na20, K20, and mixtures of Na20 and K20, up to 10% Ti02, and at least two bivalent metal oxides in the indicated proportions selected from the group consisting of up'to 25% ;Ba0, up to 10% P100, 3% to 15% 021.0, 3% t0 15% ZnO, 3% to 15% S'rO, 3% to 5% C010 and-'3%'to30% ofa mixture of SrO and CdO, the maximum proportion of either SrO or CdO in said mixture being 15%, the selected bivalent metal oxides including BaO and an oxide selected from the group consisting of SrO, CdO, and a mixture of SrO and CdO in the above-indicated proportions, the total of the bivalent metal oxides being between 15% and 50%, the softening point of the glass being below 700 0., the refractive index (11D) being between 1.57 and 1.70 and the thermal expansion coefficient being between 83 10*' and 95x10- cm. per cm. per C. between and 300 C.

7. An ophthalmic glass which comprises 33% to 60% Si02, 1% to 7% B203, 2% to 15% mm, 0.3% to 5% LizO, 1% to 15% of an alkali metal oxide selected from the group consisting of Na20, K20, and mixtures of N220 and K20, up to 8% A1202, up to 10% 'Ii02, and at least'two bivalent metal oxides in the indicated proportions selected from the group consisting of up to 25% BaO, up to 10% PhD, 3% to CaO, 3% to 15% ZnO, 3% to 15% SrO, 3% to 15% CdO, and 3% to 30% of a mixture of S10 and CdO, the maximum proportion of either SrO or CdO in said mixture being 15%, the selected bivalent metal oxides including 13:10 and an oxide selected from the group consisting of S10, 0110, and a mixture of SrO and CdO in the above-indicated proportions, the total of the bivalent metal oxides being between 15% and 50%, the

softening point of the glass being below 700 0., the refractive index (nD) being between 1.57 and 1.70 and the thermal expansion coefficient being between 83 10- and 95 10" cm. per cm. per C. between 0 and 300 C.

8. An ophthalmic glass which comprises 33% to 60% .Si02, 1% to 7% B203, 2% to 15% ZrOz, 0.3% to 5% Li2O, 1% to 15% of an alkali metal oxide selected from the group consisting of Na20, K20, and mixtures of Na and K20, and at least three bivalent metal oxides in the indicated proportions selected from the group consisting of up to BaO, up to 10% PhD, 3% to 15% CaO, 3% to 15% ZnO, 3% to 15% SrO, 3% to 15% CdO, and 3% to of a mixture of SrO and CdO, the maximum proportion of either SrO or CdO in said mixture being 15%, the selected bivalent metal oxides including BaO, Pb0 and an oxide selected from the group consisting of SrO, CdO, and a mixture of SrO and CdO in the aboveindicated proportions, the total of the bivalent metal oxides being between 15% and the softening point of the glass being below 700 C., the refractive index (nD) being between 1.57 and 1.70 and the thermal expansion coefficient being between 83 l0-' and 10- cm. per cm. per C. between 0 and 300 C.

WILLIAM H. ARMISTEAD.

No references cited.

Certificate of Correction Patent No. 2,523,264

WILLIAM H. ARMISTEAD It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows:

Column 1, line 7 for lasses read Glasses; line 46, for 70% read 7%; and that the said Letters Patent should be read as corrected above, so that the same may conform to the record of the case in the Patent Oifice.

Signed and sealed this 20th day of February, A. D. 1951.

September 26, 1950 THOMAS F. MURPHY,

A ssz'stant Commissioner of Patents. 

1. AN OPHTHALMIC GLASS WHICH COMPRISES 33% TO 60% SIO2, 1% TO 7% B2O3, 2% TO 15% TO 15% ZRO2, 0.3% TO 5% LI2O, 1% TO 15% OF AN ALKALI METAL OXIDE SELECTED FROM THE GROUP CONSISTING OF NA2O, K2O, AND MIXTURES OF NA2O AND K2O, AND AT LEAST TWO BIVALENT METAL OXIDES IN THE INDICATED PROPORTIONS SELECTED FROM THE GROUP CONSISTING OF UP TO 25% BAO, UP TO 10% PBO, 3% TO 15% CAO, 3% TO 15% ZNO, 3% TO 15% SRO, 3% TO 15% CDO, AND 3% TO 30% OF A MIXTURE OF SRO AND CDO, THE MAXIMUM PROPORTION OF EITHER SRO OR CDO IN SAID MIXTURE BEING 15%, THE SELECTED BIVALENT METAL OXIDES INCLUDING AN OXIDE SELECTED FROM THE GROUP CONSISTING OF SRO, CDO, AND A MIXTURE OF SRO AND CDO IN THE ABOVE-INDICATED PROPORTION, THE TOTAL OF THE BIVALENT METAL OXIDES BEING BETWEEN 15% AND 50%, THE SOFTENING POINT OF THE GLASS BEING BELOW 700* C., THE REFRACTIVE INDEX (ND) BEING BETWEEN 1.57 AND 1.70 AND THE THERMAL EXPANSION COEFFICIENT BEING BETWEEN 83X10**-7 AND 95X10**-7 CM. PER CM. PER *C. BETWEEN 0* C. AND 300* C. 